Toxic residues or wastes are those that because of their corrosive, reactive, explosive, toxic, flammable, infectious, radioactive characteristics may cause risk or damage to human health or to the environment. Furthermore, containers, packaging, and crates that have come into contact with toxic residues or wastes are also considered hazardous residues or wastes. Within the current environmental norms, hazardous residues are all metallic wastes or wastes containing metals like antimony, arsenic, beryllium, cadmium, lead, mercury, selenium, tellurium, thallium; wastes containing mainly inorganic constituents that may contain metals or organic matter like activated glass and catalysts, among others, and wastes containing mainly organic constituents that may contain metals and inorganic matter like thermal liquid wastes, nitrocellulose, phenolic compounds, ethers, wastes from leather tanning processes, halogenated organic solvents, wastes from the production of aliphatic halogenated hydrocarbons, tarry residues, and substances or articles contaminated with polychlorinated biphenyl (PCB), polychlorinated terphenyl (PCT), polychlorinated naphthalene (PCN), or polybrominated biphenyl (PBB) in concentrations greater than or equal to 50 mg/Kg.
Traditionally, the treatment with solvents with the purpose of destroying a wide variety of hazardous organic compounds like polychlorated biphenyls (PCBs) and pyridine has been carried out by means of incineration. However, it is common knowledge that the incineration of these compounds generates incomplete combustion byproducts that end up being more harmful than the chemicals from which they come, for which the use of this treatment process has raised growing rejection in diverse sectors of society. Additionally, incineration is a costly treatment, thus, not easily available in developing nations. This is why there is a tendency to export hazardous residues to other nations to comply with international environmental treaties.
There are numerous treatments developed to eliminate chemical residues with high organic load coming from industry, within which are the treatments under super critical conditions that have shown remarkable results. The nearest anticipations to the invention correspond to some documents disseminated on the state of the art like patent EP 0898985, which divulges a method to treat organic waste materials that comprises a first step of organic material decomposition in the shape of products of low molecular weight subjected to super critical conditions to then apply an oxidation step and decomposition of the products of low molecular weight into carbon dioxide and water, keeping the mixture of the oxidant and the products of low molecular weight in the middle in a subcritical state.
Patent EP0755361 reveals a method for treating waste waters that contain organic matter under super critical conditions (219 atmospheres and temperature between 288 and 649° C.) in the presence of hydrogen peroxide. Additionally, it includes a system which develops a process including an elongated chamber reactor that comprises a frontal portion, a rear portion, a primary reaction zone, and a secondary reaction zone between the frontal portion and rear portion. The system includes media to determine the total oxygen demand in the primary flow current or in the secondary current and control devices for the quantity of oxidizing agent injected to the reactor, as well as devices capable of measuring the total organic carbon of the reactor's output current.
U.S. Pat. No. 7,329,395 shows an apparatus to treat organic residues, comprising a tank to receive organic residues, a hydrogen peroxide storage tank, a pressure regulator, a liquid gas condenser, a collection tank, and a controller for negative pressures. The apparatus for residue treatment includes a line that permits introducing oxidizing agents like oxygen and ozone into the residue treatment zone. The treatment conducted on the liquid comprises the prior addition of sodium hydroxide followed by the addition of formic acid or ammonium to then separate the gases generated in the reaction and add an alkaline solution. Thereafter, ozone or hydrogen peroxide is added or the mixture is placed in contact with UV rays to separate gaseous decomposition products from liquid decomposition products, as well as the radionuclides through a method of ionic exchange, precipitation, or extraction. Once the whole treatment is carried out, a stable solid residue is formed and another liquid phase that can be emitted as a clean residue into sea water.
Recently, it has been suggested that hazardous organic compounds like polychlorated biphenyls (PCBs) and pyridine can be destroyed by means of oxidation in water super critical to innocuous products that can be freed directly onto the environment without additional treatment. Patent JP 2000005594 divulges a method for continuous decomposition of PCB in a reaction medium comprising sodium ethoxide, methanol, carbonate, and sodium hydroxide as catalyst. The reaction conditions correspond to a median temperature level between 100 and 250° C. to react upon nearly 98% of the chlorated compounds; particularly, temperatures between 278 and 350° C. and pressure at 100 to 120 atm are preferred.
Likewise, U.S. Pat. No. 6,162,958 reveals an oxidative decomposition process to decompose PCB, comprising the steps to make the organic matter react with an oxidizing agent like sodium hydroxide in the presence of CO2 and water. The optimal temperature of the reaction is 350° C. and the reaction pH is kept at pH 7.5 by adding NaOH. The products obtained present great corrosive capacity for which a second treatment is conducted with oxygen, air, or hydrogen peroxide.
The process for the destruction of polychlorated biphenyls (PCBs) and other hazardous compounds submitted by the invention is developed under much lower temperature conditions than the incineration processes and may be carried out in a continuous mobile unit that can be transferred directly to the site where the existence of hazardous compounds is identified, eliminating the need for specialized transport and the risks associated with such.
The continuous mobile unit of the invention permits conducting the destruction of effluents or media contaminated with hazardous residue from chemical, cosmetic, and pharmaceutical industry through a process of complete oxidation in homogenous phase in the presence of water and oxygen in supercritical water, especially when the concentration of the organic substances in said aqueous effluent is very low, while it is not possible to destroy such compounds through an incineration process and often it is necessary to use techniques requiring prolonged treatment periods and high costs. For this motive, the technology developed for the treatment of hazardous residues and wastes results viable for developing nations because it solves the technical problem associated with the lack of incineration facilities complying with strict safety requirements for the elimination of hazardous organic contaminants, including polychlorated biphenyls (PCBs) and pyridine.
Also, the novel and inventive vindicated process is different from those revealed by the state of the art through the physical and chemical conditions of the medium as in the characteristics of the reactivos, such is the case of the use of water under super critical conditions to generate the elimination of wastes with diverse chemical and functional characteristics, as the case of organic residues and their mixtures (PCBs and pyridine), which according to the state of the art cause technical problems for their elimination. Furthermore, the process is carried out in a sole oxidation stage under adiabatic conditions, i.e., it does not require water cooling or a second oxidation stage, given that the whole process is developed during a relatively short term to manage destruction of organic matter represented as 99.999% total organic carbon.
Likewise, by means of an emulsifying stage a homogenous reaction phase is assured in which the contaminating products undergo complete oxidation; hence, there is certainty that CO2 and gases are generated with the consequential increase in process efficiency.
Through the combined control of the pressure required, that is, until reaching a maximum of 240 atm for at least 30 seconds, as well as the incorporation of emulsifying agents onto the process and the temperature control within a range between 350 and 530° C., the complete transformation is assured of the halogenated and heteroaromatic hydrocarbons and other additional substances considered hazardous wastes, in order to avoid contamination of water sources and the environmental surroundings where the treatment is conducted.
Furthermore, the novel and inventive process generates the chemical transformation of the contaminating agents without it being necessary to reduce them to substances of low molecular weight to carry out the oxidation, i.e., reduce the stages necessary to cause the oxidation of the contaminating mixtures, as well as time needed to cause their destruction. Eventually, the use of heterogeneous catalysts may be considered like common metallic oxides or supported metals, for example, Fe3O4, MnO2, CuO, NiO, Al2O3, Cu3O4, and Pt that increase process efficiency.
Thus, novel and inventive process divulged does not require adding sodium hydroxide, formic acid, or ammonium to generate the conversion of ions or to separate the gases generated in the reaction; it also does not require adding an alkaline solution or a medium to gather ions produced and generated in the gas.